What exactly is Flatpak and what are its main use-cases?

I just noticed that the current update of the distribution I'm using (version 18.3 of Linux Mint) boasts supports for "Flatpak". So, I ddg'ed it and found [this Wikipedia page](https://en.wikipedia.org/wiki/Flatpak) about yet. So I understand Flatpak is some sort of sandboxing framework - but I don't see anything which suggests why it's useful and interesting for me to run all sorts of apps in "isolation" at all - unless I'm managing some physical machine offering "cloud" services. Why would I want to do this? Going on the Flatpak website, it seems like it's offering a sort of a bypass around the individual distributions' package management system + support for multiple versions of the same package. Now, the second feature I like, but isn't it just something that distro package management systems need to start supporting better? As for the first part - it sounds like the [14 competing standards situation from xkcd](https://xkcd.com/927/) . Am I misunderstanding something here? PS - How is it different than Docker, which also does a sort of a sandboxing that's not as strong as putting up a virtual machine?